JP4297656B2 - New alkenylphenol polymer - Google Patents

Description

（式中、Ｒ_１は、水素原子、または置換基を有していてもよいＣ１〜Ｃ６炭化水素基を表し、ｑは、１または２を表す。）で表される繰り返し単位、及び、
式（ＩＩ）
【化２】

〔式中、Ｒ _２ は、水素原子、または置換基を有していてもよいＣ１〜Ｃ６炭化水素基を表し、Ｘは、式（III）
【化３】

（式中、Ｙは、置換基を有していてもよいＣ１〜Ｃ４の２価炭化水素基を表し、Ｒ _３ は、Ｃ１〜Ｃ６の炭化水素基を表し、ｍは、０または１〜５のいずれかの整数を表し、ｋは、０または１〜６のいずれかの整数を表し、ｍが２以上の場合に、Ｒ _３ は、それぞれ同一または相異なっていてもよく、ｋが２以上の場合には、Ｒ _３ は、それぞれ同一または相異なっていてもよい。）で表される縮合多環式芳香族炭化水素基を含む官能基を表し、ｎは１または２を表し、ｎが２の場合、Ｘは同一または相異なっていてもよい。〕で表されるいずれかの繰返し単位を少なくとも１種以上有する繰り返し単位を有する重合体、及び
【０００６】
（２）式（Ｉ）
【化４】

（式中、Ｒ_１は、水素原子、または置換基を有していてもよいＣ１〜Ｃ６炭化水素基を表し、ｑは、１または２を表す。）で表される繰り返し単位を含む主鎖末端に、式（ＩＩＩ）
【化５】

（式中、Ｙは、置換基を有していてもよいＣ１〜Ｃ４の２価炭化水素基を表し、Ｒ _３ は、Ｃ１〜Ｃ６の炭化水素基を表し、ｍは、０または１〜５のいずれかの整数を表し、ｋは、０または１〜６のいずれかの整数を表し、ｍが２以上の場合に、Ｒ _３ は、それぞれ同一または相異なっていてもよく、ｋが２以上の場合には、Ｒ _３ は、それぞれ同一または相異なっていてもよい。）で表される縮合多環式芳香族炭化水素基を含む官能基を有することを特徴とする重合体に関する。
【０００７】
【発明の実施の形態】
本発明の重合体に含まれる式（Ｉ）で表される繰り返し単位中、Ｒ₁は、水素原子、または置換基を有していてもよいＣ１〜Ｃ６炭化水素基を表し、具体的には、メチル基、エチル基、ｎ−プロピル基、イソプロピル基、フェニル基、フルオロメチル基、トリフルオロメチル基等を例示することができる。
水酸基の置換位置は特に限定されないが、パラ位、メタ位を好ましく例示することができる。また、水酸基の数は、1個が好ましいが、場合によって２個有していてもよい。
【０００８】
本発明の重合体に含まれる縮合多環式芳香族炭化水素基は、ディープＵＶ（２４０〜２６０ｎｍ）波長領域に吸収を有するものが好ましく、具体的には、ナフタレン、アントラセン等の骨格を有する官能基を好ましく例示することができ、特に、式（ＩＩＩ）で表される官能基をさらに好ましく例示することができる。
【０００９】
式（ＩＩＩ）中、Ｙは、置換基を有していてもよいＣ１〜Ｃ４の２価炭化水素基を表し、具体的には、メチレン基、エチレン基、１−メチルエチレン基、２−プロぺニレン基等を例示することができる。
また、式（ＩＩＩ）中、Ｒ₃は、Ｃ１〜Ｃ６の炭化水素基を表わし、具体的には、メチル基、エチル基、ｎ−プロピル基、イソプロピル基等を例示することができる。
【００１０】
本発明の重合体に含まれる縮合多環式芳香族炭化水素基を有する繰り返し単位は、上記例示した縮合多環式芳香族炭化水素基を炭素原子、または酸素原子、窒素原子、リン原子等のヘテロ原子を介して、直接等、任意の結合様式で、式（Ｉ）で表わされる繰り返し単位と共に構成する繰り返し単位に結合しているものであれば、特に制限されないが、具体的には式（ＩＩ）で表わされるくり返し単位を例示することができる。
【００１１】
式（ＩＩ）中、Ｒ₂は、水素原子、または置換基を有していてもよいＣ１〜Ｃ６炭化水素基を表わし、具体的には、Ｒ₁で例示したのと同様のものを例示することができる。 Ｘ基、Ｏ−Ｘ基、ＯＨ基の置換位置は特に制限されないが、メタ位、またはパラ位が好ましい。
【００１２】
また、本発明においては、縮合多環式芳香族炭化水素基を含む官能基を、式（Ｉ）で表わされる繰り返し単位を含む主鎖末端に有することを特徴とする。この場合、縮合多環式芳香族炭化水素基を含む官能基は、炭素原子、または酸素原子、窒素原子、リン原子等のヘテロ原子を介して、直接等、任意の結合様式で該主鎖末端に結合することができる。また、縮合多環式芳香族炭化水素基を含む官能基とは、縮多環式芳香族炭化水素基を任意の結合様式で含む官能基、または、縮合多環式芳香族炭化水素基そのものを表わすこととする。
【００１３】
本発明における重合体の製造方法として、具体的には、
（１）式（ＩＶ）
【化９】

で表わされるアルケニルフェノール類を、ラジカル重合（熱重合）させた後、例えば式（Ｖ）
【化１０】

（式中、Ｚは、塩素原子、臭素原子、ヨウ素原子等の求核置換反応で脱離する基を表わす。）で表わされる縮合多環式芳香族炭化水素基を有する試薬を用いて水酸基の活性水素を置換する方法、
（２）式（ＶＩ）
【化１１】

（式中、Ｒ’は、アニオン重合、水酸基の保護基を表わす。）で表わされるアルケニルフェノール類をラジカル重合、イオン重合させ、Ｒ’基を脱保護した後、例えば式（Ｖ）で表わされる縮合多環式芳香族炭化水素基を有する試薬を用いて水酸基の活性水素を置換する方法、
（３）式（ＶＩ）で表わされるアルケニルフェノール類と式（ＶＩＩ）
【化１２】

で表わされるいずれか１種以上のアルケニルフェノール類を共重合（ラジカル重合、イオン重合）させた後、Ｒ’基の全部またはその１部を脱離させる方法、
（４）式（ＶＩ）で表わされるアルケニルフェノール類を用いてリビングアニオン重合させた後、必要に応じて１，１−ジフェニルエチレン、１，２−ジフェニルエチレン等反応させ、末端アニオンをキャップした後、例えば、式（Ｖ）で表わされる縮合多環式芳香族炭化水素基を有する試薬を反応させ、さらに、Ｒ’基を脱保護させる方法等を例示することができるが、これらの方法に限定されるものではない。
【００１４】
反応条件は、公知の反応条件を用いることができるが、例えば、上記（４）において、１，１−ジフェニルエチレンを用いて重合アニオン末端をキャップした後、式（Ｖ）で表わされる試薬を反応させる温度は、０℃から室温の範囲で行うのが好ましい。また、上記（４）の方法で、末端に縮合多環式芳香族炭化水素基を有する官能基を導入する場合において、末端が反応しない重合体との混合物として重合体を得る場合には、各製造時において、末端官能基の含有比率を一定にさせるために、予想される活性重合末端モル数以下で、用いられる例えば式（ＶＩ）で表わされる単量体に対して一定の比率だけの量を用いるのが好ましい。
【００１５】
以下、実施例を用いて本発明をさらに詳細に説明するが、本発明は実施例に限定されるものではない。
【００１６】
【実施例】
実施例１
窒素雰囲気下において、テトラヒドロフラン（以下、ＴＨＦと略す）４５０ｇとヘキサン １１０ｇの混合溶媒を−４０℃に保持し、ｎ−ブチルリチウム（以下、ＮＢＬと略す）３．５ｇ（８．５ミリモル）を加え、撹拌下、ｐ−ｔｅｒｔ−ブトキシスチレン（以下、ＰＴＢＳＴと略す）１００ｇ（５６７ミリモル）を３０分かけて滴下し、さらに反応を１時間継続し、ガスクロマトグラフィー（以下、ＧＣと略す）により反応完結を確認した。次いで、反応系に、ジフェニルエチレン（以下、ＤＰＥと略す）１．５ｇ（８．５ミリモル）を添加して３０分反応を継続した後、９‐クロロメチルアントラセン１．９ｇ（８．５ミリモル）を添加し、直ちに室温まで加温、６０分反応を継続してＧＣにより反応完結を確認した。最後に、反応液を大量のメタノール中に投入してポリマーを析出させ、濾過、洗浄後、６０℃で５時間減圧乾燥して白色粉体状のポリマーを得た。用いたモノマー総量に対する重合収率は、９９．５％であった。
このポリマーをゲル濾過クロマトグラフィー（以下、ＧＰＣと略す）により分析したところ、Ｍｎ＝１４０００、Ｍｗ／Ｍｎ＝１．０９の単分散ポリマーであった。
次に、得られたポリマー１０ｇをエタノールに溶解して３０％溶液とし、濃硫酸１ｇを加えて７０℃で３時間反応を行った後、反応液を大量の水中に投入してポリマーを析出させ、濾過、洗浄後、６０℃で５時間乾燥して白色粉体状ポリマー ６８ｇを得た。
このポリマーのＧＰＣ分析を行ったところ、Ｍｎ＝９８００、Ｍｗ／Ｍｎ＝１．０９の単分散ポリマーであり、¹³ＣＮＭＲによりｔｅｒｔ−ブチル基に由来するシグナルが消失したことから、脱ブチル化反応が完結していることが確認できた。一方、¹ＨＮＭＲにより、６．２〜６．８ｐｐｍにポリｐ−ヒドロキシスチレンのベンゼン環基由来のシグナル、７．２ｐｐｍ付近にＤＰＥのベンゼン環基由来のシグナル、６．８〜８．５ｐｐｍにアントラセン環由来のシグナルが観察せれ、それぞれの積分比から、ポリマー中にＤＰＥとアントラセン環のユニットがそれぞれ１分子が含まれていることを確認できた。
以上のことから、反応およびその後の脱離反応は目的通り行われ、ｐ−ヒドロキシスチレンセグメントの末端にアントラセン環を１分子有する狹分散アルケニルフェノール系重合体が生成したことを確認した。
【００１７】
実施例２
ＶＰ−８０００（日本曹達（株）社製、Ｍｎ＝１１，００、Ｍｎ／Ｍｗ＝１．０９）６０．１ｇ（０．５ｍｏｌ）、１−クロロメチルナフタレン１３．３ｇ（７５ｍｍｏｌ）、沃化ナトリウム０．８ｇ（５ｍｍｏｌ）、テトラブチルアンモニウムブロマイド（ＴＢＡＢ）１．６１ｇ（５ｍｍｏｌ）、炭酸カリウム１３．８ｇ（０．１ｍｏｌ）、ＭＥＫ３００ｇの混合物を、７５℃で６．５時間反応させ、薄層クロマトグラフィーで１−クロロメチルナフタレンのスポットがなくなったので反応を終了させた。
得られた反応液を濾過し、塩酸で酸性にした後、ヘキサンに注入し、ポリマーを析出させ、濾過後減圧乾燥させた。得られたポリマーをＴＨＦに溶解させ、蒸留水に落としポリマーを析出させ、濾過後乾燥した。
得られたポリマーのＧＰＣおよびＮＭＲ測定を行った。その結果、ＧＰＣからは形状がほとんど変化していないこと、ＮＭＲからはナフチルメチル基の導入率１３．５％（反応率：９０％）であることがわかり、反応がほぼ定量的に進行し、しかも副反応がおこらないことがわかった。膜厚１μｍ時の２４８ｎｍの透過率は約２５％であった。
【００１８】
【発明の効果】
以上述べたように、本発明の重合体は、新規な構造を有しており、従来とは異なる機能が期待できる重合体であり、産業上の利用価値は高いと言える。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel alkenylphenol polymer having hydroxystyrene or substituted hydroxystyrene as a monomer unit.
[0002]
[Prior art]
Homopolymers, copolymers and terpolymers having hydroxystyrene or substituted hydroxystyrene as monomer units are known to be useful as photoresist compounds having low absorbance in the deep UV (240-260 nm) wavelength region.
[0003]
[Problems to be solved by the invention]
However, in order to form a more complicated pattern, a new type of photoresist compound that has never been known has been desired. The present invention aims to provide a new type of photoresist compound.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have not found a polymer having hydroxystyrenes as a main chain by appropriately modifying a condensed polycyclic aromatic hydrocarbon group. The present inventors have found that a photoresist compound having performance can be obtained and completed the present invention.
[0005]
That is, the present invention
(1) Formula (I)
[Chemical 1]

(Wherein R ₁ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a substituent, q represents 1 or 2) , and
Formula (II)
[Chemical formula 2]

[Wherein, R ₂ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a substituent, and X represents a formula (III)
[Chemical 3]

(In the formula, Y represents an optionally substituted C1-C4 divalent hydrocarbon group, R ₃ represents a C1-C6 hydrocarbon group, and m is 0 or 1-5. And k represents an integer of 0 or 1 to 6, and when m is 2 or more , each R ₃ may be the same or different, and k is 2 or more. In this case, R ₃ may be the same or different from each other.) Represents a functional group containing a condensed polycyclic aromatic hydrocarbon group represented by: n represents 1 or 2; In the case of 2, X may be the same or different. And a polymer having a repeating unit having at least one repeating unit represented by the formula:
(2) Formula (I)
[Formula 4]

(In the formula, R ₁ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a substituent, and q represents 1 or 2.) At the end, the formula (III)
[Chemical formula 5]

(In the formula, Y represents an optionally substituted C1-C4 divalent hydrocarbon group, R ₃ represents a C1-C6 hydrocarbon group, and m is 0 or 1-5. And k represents an integer of 0 or 1 to 6, and when m is 2 or more , each R ₃ may be the same or different, and k is 2 or more. In this case, R ₃ may be the same or different from each other.) A polymer having a functional group containing a condensed polycyclic aromatic hydrocarbon group represented by:
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the repeating unit represented by the formula (I) contained in the polymer of the present invention, R ₁ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a substituent, specifically, , Methyl group, ethyl group, n-propyl group, isopropyl group, phenyl group, fluoromethyl group, trifluoromethyl group, and the like.
The substitution position of the hydroxyl group is not particularly limited, but preferred examples include the para position and the meta position. Further, the number of hydroxyl groups is preferably one, but may be two in some cases.
[0008]
The condensed polycyclic aromatic hydrocarbon group contained in the polymer of the present invention preferably has an absorption in the deep UV (240 to 260 nm) wavelength region, specifically, a functional group having a skeleton such as naphthalene or anthracene. The group can be preferably exemplified, and in particular, the functional group represented by the formula (III) can be more preferably exemplified.
[0009]
In formula (III), Y represents a C1-C4 divalent hydrocarbon group which may have a substituent, and specifically includes a methylene group, an ethylene group, a 1-methylethylene group, a 2-propyl group. A penylene group etc. can be illustrated.
In formula (III), R ₃ represents a C1-C6 hydrocarbon group, and specific examples include a methyl group, an ethyl group, an n-propyl group, and an isopropyl group.
[0010]
The repeating unit having a condensed polycyclic aromatic hydrocarbon group contained in the polymer of the present invention includes the condensed polycyclic aromatic hydrocarbon group exemplified above as a carbon atom, oxygen atom, nitrogen atom, phosphorus atom, etc. Although there is no particular limitation as long as it is bonded to the repeating unit constituted together with the repeating unit represented by the formula (I) in any bonding mode such as directly via a hetero atom, specifically, the compound represented by the formula ( The repeating unit represented by II) can be illustrated.
[0011]
In formula (II), R ₂ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a substituent, and specifically, the same examples as those exemplified for R ₁ are exemplified. be able to. The substitution position of the X group, OX group and OH group is not particularly limited, but the meta position or para position is preferred.
[0012]
Moreover, in this invention, it has the functional group containing a condensed polycyclic aromatic hydrocarbon group in the principal chain terminal containing the repeating unit represented by Formula (I), It is characterized by the above-mentioned. In this case, the functional group including the condensed polycyclic aromatic hydrocarbon group is bonded to the main chain terminal in any bond mode such as directly via a carbon atom or a hetero atom such as an oxygen atom, a nitrogen atom, or a phosphorus atom. Can be combined. In addition, the functional group containing a condensed polycyclic aromatic hydrocarbon group is a functional group containing a condensed polycyclic aromatic hydrocarbon group in an arbitrary bonding mode, or a condensed polycyclic aromatic hydrocarbon group itself. To represent.
[0013]
As a method for producing a polymer in the present invention, specifically,
(1) Formula (IV)
[Chemical 9]

After the radical polymerization (thermal polymerization) of the alkenylphenol represented by the formula, for example, the formula (V)
[Chemical Formula 10]

(Wherein Z represents a group that is eliminated by a nucleophilic substitution reaction such as a chlorine atom, a bromine atom, or an iodine atom) and a hydroxyl group using a reagent having a condensed polycyclic aromatic hydrocarbon group represented by A method of replacing active hydrogen,
(2) Formula (VI)
Embedded image

(In the formula, R ′ represents an anionic polymerization, a hydroxyl protecting group.) After radical polymerization and ionic polymerization of the alkenylphenol represented by the formula (I), the R ′ group is deprotected, and then, for example, represented by the formula (V) A method of substituting active hydrogen of a hydroxyl group using a reagent having a condensed polycyclic aromatic hydrocarbon group,
(3) Alkenylphenols represented by formula (VI) and formula (VII)
Embedded image

A method in which one or more alkenylphenols represented by the formula (1) are copolymerized (radical polymerization, ionic polymerization) and then all or part of the R ′ group is eliminated,
(4) After carrying out living anion polymerization using alkenylphenols represented by formula (VI) and then reacting with 1,1-diphenylethylene, 1,2-diphenylethylene, etc. as necessary, and capping the terminal anions For example, a method of reacting a reagent having a condensed polycyclic aromatic hydrocarbon group represented by the formula (V) and further deprotecting the R ′ group can be exemplified, but the method is limited to these methods. Is not to be done.
[0014]
Known reaction conditions can be used as the reaction conditions. For example, in (4) above, the end of the polymerization anion is capped with 1,1-diphenylethylene, and then the reagent represented by the formula (V) is reacted. The temperature is preferably in the range of 0 ° C. to room temperature. In addition, in the case of introducing a functional group having a condensed polycyclic aromatic hydrocarbon group at the terminal by the method of (4) above, when obtaining a polymer as a mixture with a polymer at which the terminal does not react, In order to make the content ratio of the terminal functional group constant at the time of production, it is an amount of a certain ratio with respect to the monomer represented by the formula (VI) used, for example, below the expected number of moles of active polymerization terminals. Is preferably used.
[0015]
EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to an Example.
[0016]
【Example】
Example 1
Under a nitrogen atmosphere, a mixed solvent of 450 g of tetrahydrofuran (hereinafter abbreviated as THF) and 110 g of hexane was maintained at −40 ° C., and 3.5 g (8.5 mmol) of n-butyllithium (hereinafter abbreviated as NBL) was added. Under stirring, 100 g (567 mmol) of p-tert-butoxystyrene (hereinafter abbreviated as PTBST) was added dropwise over 30 minutes, and the reaction was continued for 1 hour, followed by reaction by gas chromatography (hereinafter abbreviated as GC). Confirmed completion. Next, 1.5 g (8.5 mmol) of diphenylethylene (hereinafter abbreviated as DPE) was added to the reaction system, and the reaction was continued for 30 minutes, and then 1.9 g (8.5 mmol) of 9-chloromethylanthracene. Was immediately heated to room temperature, the reaction was continued for 60 minutes, and the completion of the reaction was confirmed by GC. Finally, the reaction solution was put into a large amount of methanol to precipitate a polymer, filtered and washed, and then dried under reduced pressure at 60 ° C. for 5 hours to obtain a white powdery polymer. The polymerization yield based on the total amount of monomers used was 99.5%.
When this polymer was analyzed by gel filtration chromatography (hereinafter abbreviated as GPC), it was a monodisperse polymer with Mn = 14000 and Mw / Mn = 1.09.
Next, 10 g of the obtained polymer was dissolved in ethanol to make a 30% solution, 1 g of concentrated sulfuric acid was added and reacted at 70 ° C. for 3 hours, and then the reaction solution was poured into a large amount of water to precipitate the polymer. After filtration, washing and drying at 60 ° C. for 5 hours, 68 g of a white powdery polymer was obtained.
As a result of GPC analysis of this polymer, it was a monodisperse polymer with Mn = 9800 and Mw / Mn = 1.09, and the signal derived from the tert-butyl group disappeared by ¹³ CNMR. It was confirmed that it was complete. On the other hand, by ¹ HNMR, the signal derived from the benzene ring group of poly p-hydroxystyrene was observed at 6.2 to 6.8 ppm, the signal derived from the benzene ring group of DPE was around 7.2 ppm, and the anthracene was observed at 6.8 to 8.5 ppm. A ring-derived signal was observed, and from each integration ratio, it was confirmed that the polymer contained one molecule each of DPE and anthracene ring units.
From the above, the reaction and the subsequent elimination reaction were carried out as intended, and it was confirmed that a soot-dispersed alkenylphenol polymer having one anthracene ring at the end of the p-hydroxystyrene segment was produced.
[0017]
Example 2
VP-8000 (Nippon Soda Co., Ltd., Mn = 11,000, Mn / Mw = 1.09) 60.1 g (0.5 mol), 1-chloromethylnaphthalene 13.3 g (75 mmol), sodium iodide A mixture of 0.8 g (5 mmol), tetrabutylammonium bromide (TBAB) 1.61 g (5 mmol), potassium carbonate 13.8 g (0.1 mol), and MEK 300 g was reacted at 75 ° C. for 6.5 hours, and thin layer chromatography was performed. The reaction was terminated because the spot of 1-chloromethylnaphthalene disappeared by chromatography.
The obtained reaction solution was filtered, acidified with hydrochloric acid, poured into hexane, the polymer was precipitated, filtered and dried under reduced pressure. The obtained polymer was dissolved in THF, dropped into distilled water to precipitate the polymer, filtered and dried.
The obtained polymer was subjected to GPC and NMR measurements. As a result, it was found from GPC that the shape hardly changed, and from NMR it was found that the introduction rate of naphthylmethyl group was 13.5% (reaction rate: 90%), and the reaction proceeded almost quantitatively, Moreover, it was found that no side reaction occurred. The transmittance at 248 nm when the film thickness was 1 μm was about 25%.
[0018]
【The invention's effect】
As described above, the polymer of the present invention has a novel structure, is a polymer that can be expected to have a function different from the conventional one, and can be said to have high industrial utility value.

Claims (2)

Formula (I)

(Wherein R ₁ represents a hydrogen atom or a C1-C6 hydrocarbon group optionally having a fluorine atom , and q represents 1 or 2), and
Formula (II)

[Wherein, R ₂ represents a hydrogen atom or a C1-C6 hydrocarbon group optionally having a fluorine atom , and X represents a formula (III)

(Wherein, Y represents a divalent hydrocarbon radical of C 1~C4, _{R 3} represents a hydrocarbon group of C1 -C6, m represents an integer of 0 or 1 to 5, k represents 0 or an integer of 1 to 6, and when m is 2 or more, R ₃ may be the same or different, and when k is 2 or more, R ₃ is Each may be the same or different from each other.) Represents a functional group containing a condensed polycyclic aromatic hydrocarbon group represented by: n represents 1 or 2, and when n is 2, X is the same or It may be different. ] The polymer which has a repeating unit which has at least 1 type of any repeating unit represented by these. Formula (I)

(In the formula, R ₁ represents a hydrogen atom or a C1-C6 hydrocarbon group which may have a fluorine atom , and q represents 1 or 2). At the end, the formula (III)

(Wherein, Y represents a divalent hydrocarbon radical of C 1~C4, _{R 3} represents a hydrocarbon group of C1 -C6, m represents an integer of 0 or 1 to 5, k represents 0 or an integer of 1 to 6, and when m is 2 or more, R ₃ may be the same or different, and when k is 2 or more, R ₃ is , Each of which may be the same or different from each other.) A polymer having a functional group containing a condensed polycyclic aromatic hydrocarbon group represented by: